Generally, for manufacturing of a laminated body by pasting various film sheets made of rubber, metal, paper, fiber, wood, glass, polyvinyl chloride, polyolefin, and the like and various substrates made of foamed materials and the like, adhesive agents containing a resin dissolved in an organic solvent have been conventionally used in many cases.
Then, for manufacturing of a laminated body, for example, a dry laminate method has been widely adopted in which an adhesive agent containing a resin dissolved in an organic solvent is applied onto a substrate, the adhesive agent is dried so as to volatilize the organic solvent, and then the substrate is pasted to another substrate.
As for an adhesive agent containing an organic solvent-based resin, mainly available are: a two-component adhesive agent that is made of a polyurethane resin serving as a base compound and having a hydroxyl group, an amide group, or the like, having an active hydrogen which is reactive to an isocyanate group, and a polyisocyanate-based curing agent; and a one-component adhesive agent that contains a polyurethane resin.
Such a two-component adhesive agent has advantages of having a long period of time (that is, an open time) from the time when the adhesive agent is dried after applied onto a substrate to the time when the adhesiveness disappears, and of having superior adhesiveness at a low temperature in a range approximately from 30 to 60° C. Accordingly, the two-component adhesive agent makes it easy to paste various substrates. In addition, since a polyurethane resin serving as the base compound and a polyisocyanate-based curing agent react with each other to have a higher-molecular weight, it is possible to obtain a laminated body having superior durability, such as heat creep resistance. However, there is a problem that a pot life of an adhesive agent bath is short because of mixing of the base compound and the curing agent. Therefore, a large amount of labor for the management of the manufacturing environment, the adhesive agent bath, and the like is required.
On the other hand, as for the one-component adhesive agent, a pot life, as a two-component adhesive agent has, of an adhesive agent bath does not substantially exist. Accordingly, the management of the manufacturing environment, the adhesive agent bath, and the like is easy. However, there is a disadvantage that the open time is short. Furthermore, the open time is largely affected by the temperature of an adhesive-coated surface after drying, and tends to be short at a low temperature in a range approximately from 30 to 60° C. although it tends to be relatively long at a high temperature. Therefore, there is a problem that a large amount of labor for the management of the drying temperature and the temperature of an adhesive-coated surface is required for performing a stable paste operation.
Furthermore, containing dimethylformamide, toluene, methyl ethyl ketone, or the like as an organic solvent, many of such adhesive agents are highly flammable and highly toxic. Therefore, there is a problem regarding risk of fire, deterioration of the working environment, and environmental contaminations of the air, water, and the like. Note that a process for collecting such organic solvents has been implemented; however, there is a problem that substantial cost for disposal and a huge amount of work are required. Moreover, a laminated body obtained by use of an adhesive agent containing a resin dissolved in an organic solvent has a risk that the organic solvent remains in the laminated body. The effects on the human body, such as the sick-building syndrome, chemical sensitivity, and skin problems, which have come to be recognized in recent years, have been acknowledged as problems.
In order to solve these problems, investigation has been conducted for shifting from an adhesive agent containing a polyurethane resin dissolved in an organic solvent to an adhesive agent containing an aqueous polyurethane resin.
As for an aqueous polyurethane resin, examples are a dispersion substance in which a polyurethane resin is forced to disperse using a surfactant, and a polyurethane resin to which hydrophilicity is added by introducing a repeating unit of polyoxyethylene into a resin structure using polyether polyol, such as polyethylene glycol. The former, however, has a problem that the quality of the laminated body is lowered due to bleed of the surfactant with time, while the latter has a problem that the heat creep resistance and water resistance are insufficient.
Meanwhile, for example, the Japanese Unexamined Patent Application Publication No. Hei 6-313024 (Document 1) discloses a polyurethane resin, as a polyurethane resin having superior water solubility and water dispersivity, which is made of a lactone-based polyester polyol obtained by subjecting lactones to a ring-opening addition polymerization reaction with dihydroxycarboxylic acid as an initiator, an organic diisocyanate, and a chain extender, and which has a carboxylic group concentration of at least 10. However, since a carboxyl group is introduced to a soft segment, a polyurethane resin such as described in Document 1 is a resin having a low agglomerating property. Accordingly, in the case of being used as an adhesive agent, although the open time is slightly lengthened, the polyurethane resin is insufficient in terms of the adhesiveness at a low temperature in a range approximately from 30 to 60° C., and the durability, such as heat creep resistance and water resistance.
Meanwhile, the Japanese Unexamined Patent Application Publication No. Sho 64-69619 (Document 2) discloses a method for manufacturing an aqueous solution or a fluid dispersion of a polyisocyanate polyaddition product having groups selected from the group consisting of a carboxylate group and a sulfonate group and an ethylene oxide unit. However, in the case of using a polyisocyanate polyaddition product such as described in Document 2 as an adhesive agent, although the adhesiveness to a substrate is improved, there is a problem that stable manufacturing is difficult due to the short open time and insufficient adhesiveness at a low temperature in a range approximately from 30 to 60° C.
As described above, as for a conventional adhesive agent containing an aqueous polyurethane resin, the open time is short, the adhesiveness, especially adhesiveness at a low temperature in a range approximately from 30 to 60° C., has not reached a satisfactory level, and labor for the management of the drying temperature and the temperature of an adhesive-coated surface required for performing a stable paste operation is not reduced. In addition, a laminated body manufactured by using such an adhesive agent has a problem of being inferior to that obtained by using an adhesive agent containing an organic solvent-based polyurethane resin in terms of not only adhesive strength but also durability, such as heat-resistance creeping property.